88 



Eventually the long reign of .the ice came to an end, and 

 the glaciers slowly melted away, leaving behind the debris, 

 which had been brought from the regions to the north. 

 Thus, when the land was again uncovered, a mantle of drift 

 was spread over it, filling the ravines and smaller valleys 

 which had been cut by the pre-glacial streams. The great 

 valley now occupied by Lake Erie was filled up to a con- 

 siderable extent, and its continuation through the Dundas 

 valley into the valley of Lake Ontario was cut off by the 

 drift. The old channel of the preglacial Idlewood River was 

 also filled in bv drift. All this, however, did not appear at 

 first, for as long as the ice filled the Ontario valley, the 

 drainage of the water, resulting from the melting ice, was 

 impossible in the present direction, and it accumulated, 

 forming a long lake at the front of the ice sheet. This lake, 

 vyrhich Spencer has named Lake Warren, increased in size 

 until its w^aters finally began to overflow across the lowest 

 point on the southern watershed, which happened to be 

 near where Chicago now stands. Thus the drainage of this 

 great lake was into the Mississippi, for a long time. The 

 beaches built by this old lake can be seen a short distance 

 behind the present beach of Lake Erie, running southward 

 through Hamburgh, and crossing the present gorge of 

 Eighteen Alile Creek beyond the forks.* When, through 

 continued melting of the ice, the Mohawk, and later the St. 

 Lawrence valleys were opened, the drainage went by these 

 channels, and the water in Lake Erie was lowered to near 

 its present level. Then the waves began their work of 

 cutting into the land leaving the cliffs, now exposed on 

 the shore, which in some places are formed of the bed 

 rock, and in others of the drift-heaps left by the ice in the 

 valleys. 



'Leverett, Am. Jonrn. Science, July, 1 895, gives a map of the taeacbes. 



